1. Field of the Invention
The present invention relates to a three-dimensional measuring device.
2. Background Art
Generally, when mounting an electronic component on a printed substrate, a cream solder is first printed on a predetermined electrode pattern provided on the printed substrate. Next, the electronic component is temporarily fixed on the printed substrate based on a viscosity of the cream solder. Subsequently, the printed substrate is led to a reflow furnace, and soldering is performed by undergoing a predetermined reflow process. Recently, there is a need to inspect a printing condition of the cream solder in a step before being led to the reflow furnace, and a three-dimensional measuring device is sometimes used on an occasion of such inspection.
In recent years, various three-dimensional measuring devices of a so-called non-contact type that use light are proposed, and a technique relating to a three-dimensional measuring device using a phase shift method is proposed, for example.
In the three-dimensional measuring device using a phase shift method, a pattern light having a light intensity distribution in a sine wave shape (banded shape) is irradiated to an object to be measured (in this case, the printed substrate) by an irradiation means configured by a combination of a light source and a filter of a sine wave pattern. The object is then observed using an imaging means disposed directly above a point on the substrate. As the imaging means, a CCD camera or the like configured by a lens, an imaging element, and the like is used. In this case, an intensity I of a light of a point to be measured P on a screen is given in the formula below.I=B+A·cos φ[B: direct current light noise (offset component), A: contrast of the sine wave (reflection rate), φ: phase given by unevenness of the object]
At this time, the pattern light is moved; the phase is changed to, for example, four steps (φ+0, φ+π/2, φ+π, φ+3π/2); images having intensity distributions of I1, I2, I3, and I4 are incorporated; and a modulation amount (position information for deriving a height) θ is sought based on the formula described below.θ=arctan {(I4−I2)/(I1−I3)}
This modulation amount θ is used to find a three-dimensional coordinate (X, Y, Z) of the point to be measured P of the cream solder or the like on the printed substrate, which coordinate is used to measure a three-dimensional shape of the object to be measured, especially a height thereof.
However, there is concern that acquiring more accurate data for each portion under a pattern light of the same brightness becomes difficult due to differing reflection rates of light and the like in the printed portion of the cream solder on the printed substrate (solder print region) and in other portions (background regions).
For example, concerning the solder print region that has a comparatively high reflection rate, there is concern that more accurate height measurement becomes difficult if the brightness of the pattern light is too high, causing a brightness saturation state (saturation) in pixels corresponding to the solder print region in the image data imaged by the imaging means. Meanwhile, concerning the background region that has a comparatively low reflection rate, there is concern that height measurement becomes difficult if the brightness of the pattern light is too low, thereby reducing a difference between light and dark (brightness difference) in the pattern light in the image data.
In contrast, in recent years, a technique for suitably performing height measurement by separately performing imaging under imaging conditions (irradiation brightness) suited to the solder print region and imaging under imaging conditions suited to the background region (See, e.g., Patent Document 1).